Isolation and Identification of Endophytic Bacteria from the Roots of Brassica Napus and the Screening for the Probiotic Effects of Plants

The endophytic bacterial strains were isolated and identified from the roots of Brassica napus, and their growth promotion and antibacterial potential and mechanism were detected and evaluated, thus to provide the basis for the development of microbial fertilizers with the abilities of plant growth promotion and disease prevention. By taking Brassica napus as the research object, the endophytic bacteria in the roots of Brassica napus were isolated and identified by the isolation and purification and 16S rRNA gene amplification. The probiotic characteristics of lignocellulose, such as the degradation ability, growth-promoting effect and antibacterial activity, and its mechanism were further analyzed by using the plate method, enzyme activity method and antibacterial test. The results showed that 14 strains of endophytic bacteria were selected and purified from the roots of Brassica napus according to the morphology, color and size of bacterial colonies. By 16S rRNA gene sequencing and identification & analysis, they were Pseudomonas, Escherichia coli, Bacillus, Staphylococcus and Lelliottia. Among the 14 isolated and purified endophytic strains, all the strains except Y-7 and Y-8 had significant xylanase activity, and all the strains except Y-1, Y-7, Y-8, Y-9 and Y-10 had the cellulose decomposition ability. The preliminary screening and evaluation on the plant probiotic effects of the 14 endophytic strains were further carried out, and the iron carrier-producing strains including strain Y-2, Y-4, Y-6, Y-10, Y-11, Y-13 and Y-14 were obtained, and the azotobacters including strain Y-1, Y-2, Y-10, Y-13 and Y-14 with stable nitrogen fixation ability were also obtained. In the screening of antagonistic endophytic bacteria, the strains Y-1, Y-6, Y-7, Y-8 and Y-12 against Escherichia coli, the strains Y-3 and Y-4 against Staphylococcus aureus, the strain Y-1 against Bacillus subtilis and the strains Y-3, Y-4, Y-6, Y-9, Y-10 and Y-14 against Aspergillus niger were obtained. Most of the endophytic bacteria isolated from the roots of Brassica napus had certain ability of lignocellulose degradation. The endophytic bacteria isolated from the roots of Brassica napus exhibited a wide range of probiotic properties such as growth promotion and bacteriostatic activity, which might be related to their abilities to produce iron carriers & IAA and the nitrogen fixation ability. The results showed that the endophytic bacteria from the roots of Brassica napus could be used as the important source for screening and developing the microbial agents with the abilities of plant growth promotion and disease prevention and control.